P799: SYNERGISTIC ANTITUMOR ACTIVITY OF THE BCMA 2 + 1 T CELL ENGAGER (TCE) ALNUCTAMAB (ALNUC; BMS-986349; CC-93269) AND CELMOD AGENTS IN MULTIPLE MYELOMA (MM) PRECLINICAL MODELS
Authors: Bruno Paiva, Bonny Gaffney, Kelven Burnett, Paola Castiglioni, Michael Angelo, Daniel W. Pierce, Isaac Boss
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Cereblon E3 ligase modulator (CELMoD®) agents, including classic immunomodulatory (IMiD®) agents, have shown antitumor activity in MM. ALNUC is an asymmetric 2-arm, humanized IgG TCE that binds to BCMA and CD3ε in a 2 + 1 format. ALNUC mediates myeloma tumor cell killing by recruiting T cells to BCMA-expressing target cells, leading to immune synapse formation and T cell cytotoxic activity. Combining CELMoD agents with ALNUC may enhance antitumor activity. Aims: Evaluate the anti-MM potential of ALNUC+pomalidomide (POM) and novel CELMoD agents mezigdomide (MEZI) and iberdomide (IBER) in preclinical models. Methods: To evaluate effects of IMiD and CELMoD agents on ALNUC-mediated T cell anti-MM activity, healthy donor (HD) T cells and/or BCMA-expressing MM cell lines were pretreated with POM, MEZI, IBER, or DMSO for 16 h (T cells) or 72 h (MM cells) prior to co-culture; ALNUC was then added for 72 h and T cell activation and MM target cell depletion were measured. To evaluate IMiD and CELMoD agent effects on artificially exhausted T cells, HD CD3+ T cells were pretreated with anti-CD3/CD28 beads and POM, MEZI, IBER, or DMSO for 7 d prior to co-culture with MM cells and ALNUC. To determine if CELMoD treatment could reverse T cell dysfunction in patients (pts) with R/R MM, pretreatment PBMCs from pts with MM who had response (n=2) or nonresponse (n=3) to ALNUC in a phase 1 trial (NCT03486067) were co-cultured with H929 cells. Co-cultures were pretreated with MEZI 1 nM for 24 h prior to adding ALNUC. Flow cytometry was used to evaluate T cell proliferation and activation and MM cell apoptosis in all co-culture models. The effects of concurrent and sequential MEZI and ALNUC were studied in a humanized mouse H929 MM xenograft model. Results: In co-cultures with HD T cells, pretreatment of MM cells with MEZI, IBER, and POM increased ALNUC-induced tumor-cell killing potency and efficacy, resulting in IC50 decreases and greater reductions of MM cells across all cell lines vs ALNUC alone. ALNUC antitumor activity against the OPM-2 cell line was also enhanced by pre-treating T cells with MEZI and IBER, but not POM. Overall, MEZI showed the greatest enhancement of ALNUC-mediated activity in this in vitro model. In artificially exhausted HD T cells, enhanced antitumor activity was observed with MEZI and IBER, but not POM, vs DMSO. Based on the strong activity of MEZI in vitro, its ability to enhance ALNUC antitumor activity was tested in a humanized mouse MM xenograft model. Priming or concurrent treatment with MEZI enhanced T cell activation, promoted T cell infiltration of tumor tissue, and increased ALNUC-induced tumor clearance. The ability of MEZI to enhance ALNUC-mediated T-cell function was also examined in a co-culture model using MM pt-derived PBMCs harvested before ALNUC treatment. Pretreatment with MEZI increased ALNUC-mediated antitumor activity vs control in samples from both responder and nonresponder pts. Summary/Conclusion: The combination of ALNUC with novel CELMoD agents showed enhanced T cell mediated antitumor activity in both in vitro and ex vivo MM models. MEZI showed the greatest ability to enhance TCE-mediated antitumor activity while reversing artificial T cell dysfunction/exhaustion in vitro. Priming and concurrent treatment with MEZI enhanced ALNUC-induced T cell infiltration and activation in a MM xenograft model. The ability of MEZI to enhance ALNUC T cell antitumor function was confirmed using PBMCs from ALNUC monotherapy-treated pts with MM. These results provide a strong biological rationale for combining MEZI or IBER with ALNUC in the clinic to enhance responses in pts with MM. Keywords: Bispecific, Multiple myeloma, B-cell maturation antigen, Imids